1. Field of the Invention
The present invention is related to a dynamic balance-testing method for a golf club shaft. More particularly, the present invention is related to the dynamic balance-testing method to measure a lateral flexibility by static force for determining a preferred striking direction of the golf club shaft.
2. Description of the Related Art
Generally, isotropy quality of a golf club shaft determines a dynamic balance character for striking. The more the golf club shaft has a high character of dynamic balance, the more it accomplishes a striking aspect, such as a striking accuracy and a striking distance. It means that a high character of dynamic balance minimizes a lateral component of force (lateral deformation) and vibration. However, a conventional manufacture method cannot ensure perfect straightness and isotropy of the golf club shaft, particularly a carbon fiber shaft. Accordingly, some non-isotropy of the golf club shaft is inevitable and results in some unbalance of the dynamic balance character. To this end, a golf club shaft must measure its isotropy on a circle with respect to an axis prior to being combined with a golf club head. An operator determines a desired striking direction of the golf club shaft by measuring and searching a minimum lateral component of force. This is regarded as a reference of striking aspect for improvement.
Referring to FIGS. 1, 1A and 1B, a conventional dynamic balance-testing method adopts a measuring manner that shakes a golf club shaft 10 for measuring dynamic balance character. First, an end of the golf club shaft 10 is fixed on a damper 20. Subsequently, a constant force acts on the other end of the golf club shaft 10 along a direction P1, as shown in FIGS, 1 and 1A. Once the force is removed from the golf club shaft 10, the end of the golf club shaft 10 causes a vibration. Frequency of vibration is measured within a predetermined time and movement of the golf club shaft 10 is determined to maintain along a straight-line motion. Second, the golf club shaft 10 is rotated to other directions P2–P12 to process previous measurements, including frequency and straight motion, as shown in FIGS. 1 and 1B. Subsequent to testing, the frequencies and the straight motions of the golf club shaft 10 are analyzed. For example, if the frequency between the two opposite directions P2 and P8 is minimum, a line running from P2 to P8 becomes a minimum lateral component of force and obtains a perfect dynamic balance that may enhance striking aspect.
Although the above-mentioned method is widely used in the industry, it prolongs the process time for testing. In addition, a track of the vibrational movement of the golf club shaft 10 cannot be confined within a single degree of freedom due to its nonisotropy. Accordingly, observing the track of the golf club head 10, it is gradually changed to a rotation from a straightline motion that may result in an error of the observational measure and fail to determine an exact direction of isotropy. Hence, there is a need for an improvement of the dynamic balance-testing method for a golf club shaft.
The present invention intends to provide a dynamic balance-testing method which bends an end of a golf club shaft a constant displacement. The dynamic balance-testing method employs a dynamometer to measure a reacting force acted from the bent end of the golf club shaft. Subsequently, the reacting forces of the golf club shaft are measured in predetermined directions so that a chart of distribution of the reacting force is obtained. Thereby, a minimum difference of the reacting forces on two opposite directions is calculated to obtain a striking direction in such a way to mitigate and overcome the above problem.